1. Field of the Invention
The invention pertains to the field of robotic systems. More particularly, the invention pertains to methods for locating an object in the vicinity of a robot and sensing the object position, orientation, contour, and features and methods for autonomously monitoring a robotic system object sensing apparatus for inaccuracies and compensating for any detected inaccuracies.
2. Description of Related Art
A robotic system typically includes one or more robots, tools wielded by the robot, sensors that enable the position of the robot to be sensed or stepper motors that move the positioning joints in steps to discrete angles or locations, firmware built into a robot controller that causes the robot to move in response to commands delivered to the controller, and software that sends commands to the robot controller to cause the robot to perform desired operations.
Robotic systems are employed in automated manufacturing operations in many situations, for example in factories. Of these robotic systems, some are dedicated to a particular task that is performed repetitively with respect to objects without any alteration in robot motion from object to object. Other robotic systems require alteration of the motion of a robot based on variations in object size, orientation, color, or other object characteristics. When a robotic system is designed to perform a particular task on objects whose characteristics vary from object to object, sensors and software are required to enable and control the robotic system to perform that task.
A pulse/echo layer thickness gauge is a measurement device that makes accurate measurements of the thicknesses of coatings applied to manufactured materials. A common application for pulse/echo layer thickness gauges is the measurement of the thickness of paint coatings applied to automotive vehicle bodies. A robotic pulse/echo layer thickness system is a robotic system to which a pulse/echo layer thickness gauge is added. The pulse/echo layer thickness gauge is thus the tool that is manipulated by the robotic system for the purpose of measuring coatings on materials. The entire robotic pulse/echo layer thickness system thus includes one or more industrial robots, one or more distance measurement sensors mounted to the end of the arm of each robot, computer programs that control the robots, and a pulse/echo layer thickness ‘tool’ mounted to the end of each robot arm.
The pulse/echo layer thickness tool held by each robot includes an ultrasonic transducer. In order to make a measurement, the pulse/echo layer thickness transducer is placed into contact with the test surface with the transducer oriented normal to the surface and the front face of the transducer in contact with the surface. This placement may be difficult for a robotic system to accomplish when the surface position, orientation, and surface contour relative to the robot are not known a priori.
Other applications require similar robotic system capabilities. For example, some color-measurement gauges require placement of instrumentation either above or against a surface. Surface appearance gauges require the positioning of an instrument at a precise distance and orientation from the surface and additionally require the instrument to be moved parallel to the surface contour.
Surface detection and alignment devices and methods in robotic systems are known in the art.    U.S. Pat. No. 3,967,242, entitled “Automatic Working Machine” and issued to Isoo et al. on Jun. 29, 1976, discloses a machine for determining the location and contour of an object from a television image.
U.S. Pat. No. 4,166,543, entitled “Method and Means for Controlling an Industrial Robot” and issued to Dahlstrom on Sep. 4, 1979, discloses methods for detecting and avoiding objects in a pathway moving from a first point to a second predetermined point.
U.S. Pat. No. 4,611,296, entitled “Manipulation Device Such as an Industrial Robot Having at Least One Sensor” and issued to Niedermayr on Sep. 9, 1986, discloses a robotic system with a manipulation device with sensors to provide tactile and force feedback.
U.S. Pat. No. 4,674,057, entitled “Ultrasonic Ranging Control System for Industrial Robots” and issued to Caughman et al. on Jun. 16, 1987, discloses a safety system for detecting unexpected objects in the intended path of a robot using an array of sensors and for stopping robot movement upon such detection.
U.S. Pat. No. 5,714,674, entitled “Reference Position Determination Method for Industrial Robot” and issued to Tsukuda et al. on Feb. 3, 1998, discloses a reference position system using keys and grooves to physically ensure the robot is in a predetermined reference position.
U.S. Pat. No. 6,138,494, entitled “Robot Calibration Tool and Method” and issued to Lee et al. on Oct. 31, 2000, discloses a clear calibration disc the size and shape of a semiconductor wafer used to calibrate the robot for semiconductor manufacturing.
U.S. Pat. No. 6,317,994, entitled “Robot Alignment Apparatus and Method for Using Same” and issued to Mangelsen et al. on Nov. 20, 2001, discloses a robot alignment method using a pointer and a post with a sleeve to confirm alignment.
U.S. Pat. No. 6,563,130, entitled “Distance Tracking Control System for Single Pass Topographical Mapping” and issued to Dworkowski et al. on May 13, 2003, discloses a robotic control system for a laser-cutting application of limp materials in which the material to be cut is placed at a fairly well-controlled position relative to the laser. The control system maintains the cutting head of the laser at a constant distance from the material as it is being cut. The control system measures the distance to the material and continually adjusts the laser cutting head as surface irregularities pass by the laser to produce sharper and more precise cuts. The control system uses laser-based distance sensors to measure the distance to the material surface.
U.S. Pat. No. 4,718,023 and U.S. Pat. No. 4,821,206, both entitled “Ultrasonic Apparatus for Positioning a Robot Hand” and issued to Arora on Jan. 5, 1988 and Apr. 11, 1989 respectively, disclose a robot object sensing apparatus using multiple receivers for locating an object, sensing the orientation of the object surface, and determining the distance to the surface. This apparatus accomplishes the task of locating an object surface that may not be detectable by any one distance sensor by using an approximate position sensing system using multiple distance sensors in multiple orientations. Once the object is sensed by one or more of the multiple sensors in the approximate position sensing system, the orientation of the object surface and the distance to the object surface is sensed by using a separate set of multiple distance sensors that are part of a precision position sensing system.
There are some significant limitations with the prior art described above, in which multiple sensors in multiple orientations are utilized to detect the location and orientation of an object. In many robotic applications, such as those in which a robot is wielding multiple tools, it may not be possible to find a manner in which one or more tools, in combination with multiple distance sensors that need to be mounted in multiple orientations, can be mounted together on the robot such that none of the viewing ranges of the sensors are obstructed by any of the tools.
Another issue with one or more tools being mounted to the robot in combination with multiple distance sensors in multiple orientations is the limitations that these multiple tool and sensor arrangements impose on the ability of the robot to orient one or more tools relative to a work surface to perform a particular task. Work objects may have numerous varied orientations of surfaces relative to the robot. The surfaces may also be located at various distances from the robot. ‘Reach’ is the ability of a robot to successfully orient one or more tools with respect to the various work surface locations so that the tools can perform a work operation on or over the object surface. Tools are often mounted and arranged on a robot in orientations that optimize the reach capability of the robot. Multiple distance sensors compete with the one or more tools for mounting space and mounting orientations on the robot. The resulting sensor and tool mounting arrangements may degrade the reach capability of the robot and tools.
The use of multiple distance sensors also imposes a requirement that the multiple distance sensors be periodically checked to ensure that they are calibrated and in agreement with each other. For example, a set of three distance sensors is often required in order to sense the orientation of an object surface in three-dimensional space. If one or more of these three distance sensors are out of calibration relative to the other sensors, then there will be errors in the sensed orientation.
The above references are hereby incorporated by reference herein.